Shear-sensitive injectable materials have a variety of medical applications. These materials may be used as bulking agents to strengthen tissues weakened by old age and/or disease, as implants to contour overlying tissue (e.g., in plastic surgery applications), or as prosthetic implants, acting as replacement tissue. In some instances, it is desirable to use a shear-sensitive injectable material as an embolic, for example, in the occlusion of abnormal blood vessels. Typical shear-sensitive injectable materials comprise a cross-linked polysaccharide or hydrogel, a carrier (typically a hydrophobic material such as oil), and matrix materials, providing paste-like compounds useful to bulk up tissue.
Current methods and delivery systems for delivering shear-sensitive injectable materials to a tissue, or to a space adjacent to a tissue, have certain disadvantages. A typical delivery system used is a syringe comprising a tube and a plunger. During the injection process, the carrier/hydrophobic material has a tendency to separate from the matrix material within the tube of the syringe, resulting in carrier-only injection into a tissue. Separation may be caused by a number of factors including shelf-life, material separation, excessive pressure in the syringe applied by the plunger, pushing the carrier/hydrophobic material ahead of the matrix material, or the use of an injection needle having a diameter which is too small. When a carrier is not well mixed, the matrix material is difficult to advance through the syringe with the plunger. Ultimately, the physician is unable to gauge properly the amount of bulking material he or she is actually injecting, resulting in the necessity for multiple treatments and discomfort to the patient.